Trump says unity is nice, but not essential

With a growing number of prominent Republicans refusing to fall in line, Donald Trump is standing firm in his assertion that the Republican Party doesn't have to be unified because he will gain Democratic votes to win in the fall.

"I think it would be better if it were unified, I think it would be - there would be something good about it," Trump said in an interview with ABC's This Week on Sunday. "But I don't think it actually has to be unified in the traditional sense."

George H.W. Bush and his son, George W. Bush, the only former Republican presidents still living, said they would not back Trump's candidacy. Two former Trump rivals for the nomination, Florida Governor Jeb Bush and South Carolina Senator Lindsey Graham, are among those who have also said they don't plan to back Trump.